A bit holder of known type may be found in German Patent Disclosure DE-C1 29 54 400, for instance. There, a bore that discharges radially into a joint between the bit holder and a sleeve subject to wear was used for forcing in hydraulic fluid, especially hydraulic oil, so as to make the sleeve easier to pull out. In such a bit holder the bit was received so as to be movably supported in the axial direction. The forces of reaction were partly absorbed by an annular flangelike shoulder of the bit bushing; with the bushing embodied essentially cylindrically, it was intrinsically impossible to entirely preclude axial reciprocation of the bushing. The bushing was designed as a part subject to wear, and with such an embodiment, replacing the part made it possible to lengthen the service life of a bit holder multiple times.
Other embodiments with axially displaceable round-shaft bits that are rotatably supported in a bushing disposed in a bit holder may be found in Austrian Patent 386 252, for instance. In the device known from this reference, the axial inward displacement of the bit was limited by its striking a collar of the bushing. To prevent loosening of the bushing under impact strain, an external thread was provided on the bushing, and the thread was screwed to an internal thread of the bit holder.
One feature common to all the known embodiments is that although loosening of the bushing in the bit is intended to be avoided to the maximum possible extent, conversely simple detachability of the bushing is intended to be assured. In all the known embodiments, reaction forces of the bit were absorbed on annular-edgelike stop shoulders of the bushings, and in this way an embodiment was never created in which there is a common composite body between the bushing and the bit holder, in which body it is possible to preclude a relative sliding motion during operation.